The present invention concern a welding system for welding a projection bolt composed of a shaft, a flange and a projection to a sheet-like work.
In the Japanese Patent Publication No. 2509103 is disclosed a technology of forming a receiving hole in which to insert the shaft of a projection bolt in a movable electrode so that the projection bolt held in the movable electrode is welded to a work such as steel sheet with an advancement of that electrode.
With the prior art as described above, the work must be moved in the case of a large work such as floor panel of automobile, etc. because the welding system itself is of stationary type, and the mechanism for it becomes extremely large in scale and, therefore, impracticable. As alternative, one may think of adopting a movable type welding system, but in that case special consideration must be given to the unit feeding projection bolts to the electrode. Namely, in installing a projection bolt feed unit on the welding system, a system advantageous for the feed to electrode must be applied. Moreover, the projection bolt composed of a shaft, a flange and a projection for welding must be held accurately, to obtain a good welding quality.
The projection bolt welding system according to the present invention is a system for welding a projection bolt composed of a shaft, a flange formed at one end of the shaft and a projection for welding formed on the surface of the flange opposite to the shaft to a sheet-like work, comprising a welding frame which is made to move to required point by a robot system, a movable electrode and a fixed electrode installed on the welding frame, a receiving hole being formed in one of the two electrodes for receiving the shaft of the projection bolt, and a projection bolt feed unit attached to the welding frame. The shaft is inserted in the receiving hole from the projection bolt feed unit and, in that state, the welding frame moves to a prescribed point of the work where the projection for welding and the work are pressed against each other to energize and perform welding. Since the welding frame and the projection bolt feed unit are integrated into a single unit as described above, it becomes possible to move the electrode to the target point on the work to complete welding while feeding bolts to the electrode and, therefore, there is no need of installing any special equipment for moving a large work.
The projection bolt feed unit may be disposed behind the electrode as seen from the direction of advancement of the welding frame. When the welding frame advances toward the work, it is important that the electrode holding the projection bolt reaches the welding point at its foremost position. It means that the projection bolt feed unit must not put any obstacle to the advancement of the welding frame. If the projection bolt feed unit was installed in front of the welding frame, this feed unit would interfere with other members in the surrounding area, making it impossible to perform welding of the bolt at any desired point. Since there is no problem of interference by the feed unit as explained above, a good welding behaviour is realized.
The projection bolt feed unit may comprise a forward-backward moving feed rod, a holding head attached to the feed rod, and a drive unit for inserting the shaft of projection bolt into the receiving hole. Since the forward-backward moving feed rod protrudes from or retreats into the welding frame, the projection bolt fastened to the holding head is transferred successfully to a position between the two electrodes. Especially, as the shaft stops advancement of the feed rod at the position coaxial with the receiving hole, the movement of the shaft to the receiving hole can be made with good accuracy. The shaft, which is inserted into the receiving hole with an output of the drive unit, can ensure a feed of high reliability following the advancement of the feed rod.
The drive unit is fixed to the arm member of the welding frame, the forward-backward moving drive unit of the feed rod is fixed to the output member of the drive unit, and the feed rod is provided in a way to tilt in two directions against the arm member. With this construction, the shaft of the projection bolt held in the holding head stops at the position coaxial with the receiving hole, and is inserted into the receiving hole from that position. Because a forward-backward moving drive unit for the feed rod and a drive unit for guiding the shaft to the receiving hole are provided, the transfer of the bolt to a position between the two electrodes and the insertion of the shaft into the receiving hole can be performed accurately, and this behaviour is realized especially with the fact that the forward-backward moving drive unit is fixed to the output member of the drive unit. Moreover, since the feed rod can be tilted in two directions against the arm member, it becomes possible to move the projection bolt to a position between the two electrodes, and to attach a projection bolt feed unit to the welding frame to combine them into a single unit easily.